This invention relates to an apparatus and method for steam reforming of gaseous hydrocarbons to form a synthesis gas comprising hydrogen.
Hydrogen may be produced from hydrocarbons contained in compounds such as gasified coal, coke, oil, and oil refinery waste products as well as natural gas, biogas and other compounds using a hydrogen reforming process. A well known example of this process is steam methane reforming, wherein methane and steam are reacted at temperatures between about 400° C. and about 1000° C. in the presence of a metal catalyst to yield a synthesis gas comprising carbon monoxide and hydrogen as described in the chemical equation CH4+H2O→CO+3H2. A part of the carbon monoxide thus produced may be further converted to hydrogen and carbon dioxide by the water gas shift reaction as described in the chemical equation CO+H2O→CO2+H2 to further increase the hydrogen content of the synthesis gas. The synthesis gas containing hydrogen and carbon dioxide may then be further treated in a purification unit, such as a pressure swing adsorption unit, to separate the carbon dioxide and other unwanted constituent gases to yield a product gas having a high concentration of hydrogen.
Hydrogen reforming reactors for the industrial production of hydrogen according to the aforementioned reforming process comprise a plurality of metal tubes, each typically 7-15 cm in diameter and 9-12 meters long, that contain a granular medium, such as ceramic pellets which support the metal catalyst, for example, nickel in the form of nickel oxide (NiO). The nickel oxide reduces to nickel with hydrogen and/or methane or natural gas and becomes active for the hydrogen reforming reaction. Because the reforming reaction is endothermic, the tubes are heated within appropriate temperature limits to support the chemical reactions while not exceeding the temperature limits of the tubes.
Prior art steam reforming apparatuses and methods suffer from various disadvantages. For example, the problem of catalyst fouling due to carbon formation on the catalyst, known as “coking”, limits the efficiency of the process by limiting the minimum steam to carbon ratio of the process. It would be advantageous to reduce the steam to carbon ratio without coking of the catalyst and reduce the energy required, and thereby the cost to produce hydrogen.